This invention relates generally to a magnetic stirring device, and in particular, to a stirrer suited to stirring liquids in bottles or containers having uneven bottoms.
Magnetic stirring of liquids within a closed bottle is a well-known technique. A stirrer bar in the liquid to be stirred is moved with stirring action by a magnetic field generated outside the bottle. The magnetic field may be produced by motor-driven magnets or switched coils. The stirrers normally used in such systems are permanent magnets encased in some chemically-inert material, such as glass or plastic. Such stirrers generally are denser than the medium to be stirred and thus sink to the bottom of the container. This is undesirable in the case of bottles or containers having uneven bottoms, such as bottles with extrusions or ribs on the bottom for strength.
Floating magnetic stirrers have been described in the prior art. However, these devices all use hollow floats which float on the top of the liquid surface. If the top of the liquid is far from the bottom of the container, the means of generating the magnetic field for rotation must be located along the sides of the container, adding to complexity and cost. What is needed is a stirrer which will float just above the bottom of the container as it rotates.
In the preferred embodiment, the magnetic stirrer comprises a shell, which defines a cavity. The shell has at least one hole in its uppermost surface, the surface closest to the surface of the liquid to be mixed. The stirrer also has a plug. The plug is disposed inside the cavity defined by the shell and further comprises a channel running along its uppermost surface and its sides, so that the channel is in fluid communication with both the hole and the cavity.
Embedded in the plug is a magnetic element, such as a permanent bar magnet. When an external magnetic field is rotated beneath a container containing the stirrer, the stirrer also rotates. As the stirrer rotates, liquid is impelled through the channel and downward through the cavity, creating a vortex above the stirrer and causing the stirrer to float off the bottom of the container and hover as it rotates.